Remove an ash::Shell access from ChromeLauncherController

ChromeLauncherController is resetting the virtual keyboard when the
active user changes. However, the SessionController (which is already
in ash) can have an observer that can listen to the same event. By
making the VirtualKeyboardController a SessionObserver, we can move
the keyboard reset to the other process to make it mustash-friendly.

Bug: 826391
Change-Id: I70b622105c3bf6dd415b1eee5f0521a38b6d1bf1
Reviewed-on: https://chromium-review.googlesource.com/1100672
Commit-Queue: Blake O'Hare <blakeo@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569926}
3 files changed